A light-emitting diode (LED) is a semiconductor diode that emits light when electrically biased. LEDs produce more light per watt than incandescent bulbs, and are often used in battery powered or energy-saving devices. With the advent of High Brightness LEDs, they are becoming increasingly popular in higher power applications such as flashlights, area lighting, and regular household light sources. LED performance largely depends on the efficacy (Lumens of light emitted per watt of input power), and the current level used to drive the devices. Reliability of the LEDs depends on maintaining the semiconductor junction temperature below the temperature limit specified by the manufacturer. Driving the LED hard in high ambient temperatures may result in overheating of the LED package, resulting in poor performance and eventually leading to device failure. Consequently, adequate heat-sinking or cooling is required to maintain a long lifetime for the LED, which is especially important in applications where the LED must operate over a wide range of temperatures.
Generally, LED cooling systems rely largely on convective mechanisms to remove heat. Heat convection refers to heat transport by an external source, such as a fan. The use of passive thermally conductive materials that absorb the heat and slowly rise in temperature would be highly impractical for longer term thermal dissipation. For a non-limiting example, the size of a piece of aluminum needed to cool LEDs used in a typical lighting application for a time span of eight hours or more would be so large that the aluminum would never come to saturation and the LEDs would unacceptably spike up in temperature.
Therefore improved LED systems with improved heat-removal techniques are needed. The foregoing examples of the related art are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent upon a reading of the specification and a study of the drawings.